Method for mounting semiconductor device, as well as circuit board, electrooptic device, and electronic device

ABSTRACT

A method of forming a bonded structure comprises the steps of: mounting a semiconductor device having an electrode; a convexity protruding higher than the electrode and formed of a resin; and a conductive unit electrically coupled to the electrode and extending over the surface of the convexity, onto a specific substrate with an intermediary of a bonding material; and mounting the semiconductor device by hot pressing within a temperature range including the glass transition temperature of the resin.

RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2004-130866 filed Apr. 27, 2004 and 2005-008686 filed Jan. 17, 2005which are hereby expressly incorporated by reference herein in theirentirety.

BACKGROUND

1. Technical Field

The present invention relates to a method of forming a bonded structure,as well as a circuit board, an electro-optic device and an electronicdevice.

2. Related Art

One conventional coupling method for bonding a driver IC on a substrateof a display device is a known as chip-on-glass (COG) coupling. The COGcoupling employs a method wherein, for example, a driver IC is bonded byforming an Au-plated bump on a driver IC and then electrically couplingthe bump formed on the driver IC with an electrode terminal formed on asubstrate of a display device using a conductive bonding material suchas anisotropic conductive film (ACF) and anisotropic conductive paste(ACP) (see Japanese Unexamined Patent Publication Nos. 2-272737 and3-96921, for example).

However, with the miniaturization (pitch narrowing) of the electrodes ofa driver IC, the size of conductive particles contained in the aboveconductive bonding material such as ACF and ACP is becoming close to thesize of the gap between the electrodes described above. This sometimescauses a short circuit between the electrodes of the driver IC.Therefore, it has become difficult to mount a driver IC using aconductive bonding material.

Instead, with the pitch narrowing of electrodes of a driver IC,non-conductive films (NCF), that do not contain conductive particleshave been widely used as a substitute for conductive bonding materialssuch as ACP, ACF and the like. Further, as the bump formed on a driverIC, a resin having a core of polyimide having an excellent heatresistance is used (see Japanese Unexamined Patent Publication No.6-302606, for example).

However, since a resin protrusion made of polyimide has a high elasticmodulus lower than a driver IC bonding temperature (high temperature),the resin does not make a transformation at the time of bonding, whichhas caused a problem of reduction in coupling reliability. Morespecifically, in COG bonding, an electrode of a driver IC and anelectrode terminal on a substrate of a display device are electricallycoupled with each other using NCP. Further, the coupling is fixed andretained. However, as for a resin protrusion made of polyimideconfiguring an electrode of a driver IC, the resin is hardened andcontracted by hot pressing, making the periphery of the resin protrusiontop raised. Thus, the center of the resin protrusion top is dented(e.g., recessed) compared to the periphery. Therefore, in COG bonding,NCF stays in the recess on the resin protrusion top, which may causepoor conduction in such a region and eventually a reduction in thecoupling reliability of the entire device due to the poor conduction.

Hence, as a solution to the above problem, it is considered that, withthe use of a silicon-based resin having a low elastic modulus as a bump,the rise of the periphery of the resin protrusion top due to thetransformation of the resin at the time of bonding can be avoided andthe coupling reliability between an external electrode of a driver ICand an electrode terminal of a display device can be improved. However,there is another problem in that the typical material type of resinhaving a lower elastic modulus is generally limited to, for example,silicon.

The present invention has been developed taking the above problems intoconsideration and aims to provide a method of forming a bonded structurethat can improve the coupling reliability between a resin protrusion ofa driver IC and an electrode terminal formed on a substrate of a displaydevice, as well as a circuit board, an electro-optic device, and anelectronic device.

SUMMARY

In order to solve the above problems, the present invention provides amethod of forming a bonded structure comprising the steps of: providinga semiconductor device onto a substrate with an intermediary of abonding material, the semiconductor device having an electrode, aconvexity protruding higher than the electrode and formed of a resin,and a conductive unit electrically coupled to the electrode andspreading (extending) over the surface of the convexity; and forming thebonded structure by hot pressing within a temperature range includingthe glass transition temperature of the resin.

With such a configuration, wherein hot pressing is conducted within atemperature range including the glass transition temperature of theresin, the elastic modulus of the convexity formed of resin starts todecrease at a temperature for bonding the semiconductor device on thesubstrate. Thus, an external electrode comprising the convexity of thesemiconductor makes a transformation during the hot pressing conductedat the time of bonding, thereby assuring coupling with the electrodeterminal on the substrate. As a result, the problem of poor conductioncan be solved and the coupling reliability can be improved. Further, theavailability of NCP coupling eliminates the need of using a bondingmaterial containing anisotropic conductive particles, which leads to acost reduction. Also, the manufacturing of a convexity using a resinhaving a high elastic modulus at a room temperature becomes possible. Asa result, the choice of resin materials is widened and therefore costreduction can be achieved by using an inexpensive resin. Furthermore, byusing the above-described resin as a material for the convexity, theelastic modulus of the resin decreases at the time of bonding andtherefore bonding at a low load (force) becomes possible. Thus, theformation of a convexity on a region where there is a switching elementor the like becomes possible. This means that an electrode can be formedon any region of a semiconductor device whether or not there is aswitching element present. Moreover, in the case where the convexity isformed on a region where there is a switching element or the like, theregion where a convexity is formed in the conventional technique can bereduced, thereby enabling the overall downsizing of a semiconductordevice.

Further, in the method of forming a bonded structure according to thepresent invention, the temperature of forming a bonded structure isequal to or greater than a temperature at which an elastic modulus ofthe resin starts to decrease.

With such a configuration, wherein the semiconductor device is bonded onthe substrate at a temperature equal to or greater than the temperatureat which the elastic modulus of the resin starts to decrease, the resinmakes a transformation at the time of hot pressing for bonding thesemiconductor device on the substrate. As a result, the coupling betweenthe external electrode comprising the convexity and the conduction unitof the semiconductor device and the electrode of the substrate can beassured, and therefore the coupling reliability can be improved.

Further, in a preferable method of forming a bonded structure accordingto the present invention, the resin to be used is polyimide and thetemperature of forming the bonded structure is 200 degrees Celsius orhigher and 260 degrees Celsius or lower (i.e., between 200 and 260degrees Celsius inclusive).

The bonding temperature is set to 200 degrees Celsius or higher and 260degrees Celsius or lower because, if the bonding temperature is lowerthan 200 degrees Celsius, the convexity does not make a transformationwhen bonding the semiconductor device onto the substrate due to a highelastic modulus of the polyimide convexity, which causes poor conductionbetween the semiconductor device and the substrate, thereby hinderingthe improvement of the coupling reliability. On the other hand, if thebonding temperature is greater than 260 degrees Celsius, the bondingmaterial for fixing and retaining the semiconductor device on thesubstrate is completely hardened before the convexity starts to make atransformation. Therefore, by setting the bonding temperature to 200degrees Celsius or higher and 260 degrees Celsius or lower, where theconvexity starts to make a transformation and the bonding material doesnot start to be hardened, the external electrode comprising theconvexity and conductive unit of the semiconductor device can surely becoupled to the electrode of the substrate, which improves the couplingreliability.

Further, in a preferred method of forming a bonded structure accordingto the present invention, the resin is acrylic resin or phenolic resin.

With such a configuration, since the glass transition temperature ofacrylic resin or phenolic resin is low, the convexity starts to make atransformation before the bonding material starts to be hardened. As aresult, the external electrode comprising the electrode and convexity ofthe semiconductor device can be surely coupled to the electrode of thesubstrate, which improves the coupling reliability.

Further, a preferred method of forming a bonded structure according tothe present invention comprises the steps of: providing a plurality ofthe electrodes; forming a series of the convexities on the plurality ofelectrodes that are adjacent to each other; forming the conductive uniton the surface of the convexities corresponding to each of theelectrodes; and electrically coupling the conductive unit and theelectrode.

With such a configuration, there is no need to independently form theconvexities for respective electrodes and the time required formanufacturing can be shortened.

Further, in a preferred method of forming a bonded structure accordingto the present invention, the step of forming the conductive unitfurther comprises the steps of: forming a conductive layer bysputtering; and forming the first conductive layer by patterning theconductive layer, the first conductive layer being coupled to theelectrode and spreading over the surface of the convexity.

With such a configuration, by patterning the conductive layer formed bysputtering into a specified form, the electrode and the first conductivelayer, which is formed on the surface of the convexity, can be coupledelectrically. Here, in the present invention, the “conductive layer”means a conductive material that is deposited on the substrate beforethe conductive unit (the first conductive layer and the secondconductive layer) is formed in a specific form by patterning.

Further, in a preferred method of forming a bonded structure accordingto the present invention, the step of forming the conductive unitfurther comprises the steps of: forming the second conductive layer onthe conductive layer by plating; and forming the first conductive layerby removing part of the conductive layer that is not covered with thesecond conductive layer.

With such a configuration, the conductive unit that covers from theelectrode to the surface of the convexity can be formed in a two-layerstructure comprising the first conductive layer and the secondconductive layer. Therefore, the film thickness of the conductive unitbecomes thicker and the film strength of the conductive unit isenhanced. Thus, the conductive unit is able to follow the transformationof the convexity at the time of hot pressing for bonding, and thebreakage, short circuit and the like of the conductive unit can beavoided.

Further, in a preferred method of forming a bonded structure accordingto the present invention, the bonding material is a non-conductivebonding material.

With such a configuration, a short circuit, occurring at the time ofbonding, among the plurality of electrodes that are formed on thesemiconductor device can be prevented. As a result, the externalelectrode comprising the convexity and conductive unit of thesemiconductor device can surely be coupled to the electrode of thesubstrate, which improves the coupling reliability.

Further, the present invention is a circuit board comprising asemiconductor device manufactured by the method of forming a bondedstructure With such a configuration, a circuit board having the effectdescribed above can be provided. Furthermore, the present invention isan electro-optic device comprising the above circuit board. With such aconfiguration, an electro-optic device having the effect described abovecan be provided. Moreover, the present invention is an electronic devicecomprising the above electro-optic device. With such a configuration, anelectronic device having the effect described above can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram of a semiconductor device accordingto the first embodiment, FIG. 1B is a cross-sectional view of thesemiconductor device of FIG. 1A along line A-A, and FIG. 1C is across-sectional view of the semiconductor device of FIG. 1A along lineB-B.

FIG. 2 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 3 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 4 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 5 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 6 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 7 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 8 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 9 is a drawing of a manufacturing step of a semiconductor deviceaccording to the first embodiment.

FIG. 10 is a drawing of a manufacturing step of a semiconductor deviceaccording to the second embodiment.

FIG. 11 is a drawing of a manufacturing step of a semiconductor deviceaccording to the second embodiment.

FIG. 12 is a drawing of a manufacturing step of a semiconductor deviceaccording to the second embodiment.

FIG. 13 is an exploded perspective view of a COG liquid crystal displaydevice.

FIG. 14 is a partial enlargement of a COG liquid crystal display device.

FIG. 15 is a graph of the relation between mounting temperature andacrylic resin elastic modulus.

FIG. 16 is a schematic perspective view of the configuration of a COFliquid crystal display device.

FIG. 17 is a cross-sectional view of an organic EL panel according tothe present invention.

FIG. 18 is an external view of an electronic device according to thepresent invention.

DETAILED DESCRIPTION

First Embodiment

The first embodiment of the present invention will now be described indetail referring to the accompanying drawings. In addition, in each ofthe drawings used in the following description, the scale of each layer,member, or the like is changed as a matter of convenience to show suchlayer, member, or the like in recognizable sizes.

Semiconductor device

FIG. 1A is a partial enlarged top view of a substrate on which asemiconductor element is formed, showing a semiconductor deviceaccording to the present invention. FIG. 1B is a cross-sectional viewalong line A-A in FIG. 1A. FIG. 1C is another cross-sectional view alongline B-B in FIG. 1A. In addition, the substrate in the presentembodiment can be either a semiconductor substrate such as a siliconwafer on which a number of semiconductor chips are formed or anindependent semiconductor chip. Further, in the case of a semiconductorchip, the shape of the chip is not limited to a general rectangularparallelpiped (including a cube) but can be a sphere. Furthermore, inFIG. 1A, a protective film 3 is omitted for easier understanding of thedrawing.

As shown in FIGS. 1A to C, the semiconductor device according to thepresent embodiment is a substrate 1 (a semiconductor substrate as asemiconductor device) on which a semiconductor element is formed,comprising: an electrode 2 provided for conducting input and output ofan electric signal; the protective film 3 (a passivation film) providedfor protecting the active surface of the substrate 1; a protrusion 4 (aconvexity) made of photosensitive insulating resin and placed atapproximately the same pitch as that of the electrode 2; and a firstconductive layer 5 formed to cover the electrode 2 and the surface (thetop) of the protrusion 4.

The electrode 2 comprises, as shown in FIG. 1C, an electrode pad andwiring coupled to the electrode pad. The wiring is electrically coupledto the semiconductor element bonded on the active surface of thesubstrate 1, which is described later. The electrode 2 is formed in aplural number at specified pitches near the edges of the substrate 1. Inaddition, the electrode 2, which is formed of aluminum (Al) in thepresent embodiment, can have a laminated structure in the order of,other than Al for example, a titan (Ti) layer, a titanium nitride (TiN)layer, an aluminum/copper (AlCu) layer, and a TiN layer (a cap layer).Further, the configuration of the electrode 2 is not limited to theabove but can be altered in accordance with required electric, physical,and chemical properties.

The protective film 3, which covers the periphery of the electrode 2 andreveals the electrode pad of the electrode 2 from an opening in the samefilm, is formed of an insulating film made of silicon oxide (SiO₂),silicon nitride (SiN), polyimide resin, and the like. The film thicknessof the protective film 3 is approximately 1 μm, for example. Further,the protective film 3 is patterned in a specified shape, a rectangularshape for example, and formed separately from another protective film 3covering the adjacent electrode 2. Here, the opening for revealing theelectrode 2 can be made sufficiently smaller than that provided on theconventional semiconductor device. Specifically, the opening can be asquare (or a rectangle) of approximately 5 to 10 μm on a side. Thus, byreducing the size of the opening, an external electrode 8, which isdescribed later, can be formed in a sufficiently large size within ausual region for forming an electrode. Further, in such a case, the sizeof the electrode 2 can be the same as conventional or smaller inaccordance with the size of the opening of the protective film 3. Inaddition, it is also preferred that the protective film 3 is formedspreading over adjacent electrodes 2.

As shown in FIGS. 1A to C, the protrusion 4 is formed on the surface ofthe protective film 3 on the active surface of the substrate 1 in theshape of an approximate beheaded pyramid (i.e., truncated). Theprotrusion 4 is formed to become higher than the electrode 2 by, forexample, approximately 10 to 20 μm and has a diameter of approximately20 to 50 μm when viewed from above. In addition, the protrusion 4 isplaced at approximately the same pitch as that of the electrode 2.

Further, the protrusion 4 is made of photosensitive insulating resin,which is specifically acrylic resin. The glass transition temperature ofacrylic resin is around 220 degrees Celsius. By adjusting exposureconditions using acrylic resin, the shape of the protrusion 4 becomescontrollable. In addition, photosensitive resin materials other thanacrylic resin can also be used as the above protrusion 4. For example,the protrusion can be made of phenolic resin, silicon resin, polyimideresin, silicon-modified polyimide resin, or epoxy resin, and the like.The glass transition temperature of such resins varies with resindesign: for example, approximately 100 to 200 and several dozen degreesCelsius for phenolic resin and approximately 140 to 200 and severaldozen degrees Celsius for epoxy resin.

As shown in FIG. 1C, the first conductive layer 5 is formed continuouslycovering the protective film 3, including the opening in the protectivefilm 3, spreading over the surface of the protrusion 4, and electricallycoupled to the electrode 2. Further, the protrusion 4 and the firstconductive layer 5 formed over the surface of the protrusion 4 configurethe external electrode 8. Furthermore, the first conductive layer 5 ispatterned in a specified shape so as to become the same length as thenarrow side of the basal plane of the protrusion 4. As the firstconductive layer 5, metals such as Au, TiW, Cu, Cr, Ni, Ti, W, NiV, Al,Pd, Pb-free solder, or the like can be used. In addition, it ispreferable that the first conductive layer 5 (in the case of a laminatedstructure, at least one layer) is formed using a material having ahigher corrosion resistance than that of the electrode, such as Cu, TiWand Cr, for example. This is because electrical defects can be preventedby keeping the electrode from corroding.

Method for manufacturing a semiconductor device

Next, a method for manufacturing a semiconductor device according to thepresent invention and bonding the manufactured semiconductor device on awiring board will be described in detail referring to the accompanyingdrawings. FIGS. 2 to 9 are cross-sectional views corresponding to FIG.1C, that is, cross-sectional views corresponding to the cross-sectionalviews along the line B-B in FIG. 1A.

First, as shown in FIG. 2, a plurality of electrodes 2 are formed atspecified positions on the active surface of the substrate 1. Further,the protective film 3 is formed with the electrodes 2 revealed. Theprotective film 3 is formed by first depositing silicon oxide (SiO₂),silicon nitride (SiN), or the like on the substrate 1 including theelectrodes 2. Then, a photoresist layer is formed on the SiO₂ by spincoating, dipping, spray coating, or the like, followed by exposure anddevelopment (photolithography) conducted using a mask on which aspecified pattern is formed. After that, etching is performed to thedeposited SiO₂ using the photoresist pattern, which is patterned inaccordance with the specified shape, as a mask. With such an etchingmethod, the protective film 3 having an opening for revealing theelectrode 2 is obtained. Here, it is preferable to employ dry etching.Especially, reactive ion etching (RIE) is suitable. However, wet etchingcan also be employed. In addition, after forming the opening asdescribed above, the photoresist pattern is removed using a stripperliquid, and the like.

Next, as shown in FIG. 3, a resin layer 4 a is formed by applying aresin for configuring the protrusion 4, that is, an acrylic resin tobecome positive photoresist, on the protective film 3 by the thicknessof, for example, approximately 10 to 20 μm and further prebaking. Then,as shown in FIG. 4, a mask 9 is positioned at a specified position onthe resin layer 4 a. The mask 9 to be used is a glass substrate, onwhich a light shielding film such as Cr, and the like is formed, and hasa round opening 9 a placed corresponding to the top-view shape of eachhemispherical protrusion 4 to be formed. In addition, the positioning ofthe mask 9 is conducted so that the opening 9 a comes above the pointwhere the protrusion 4 is to be formed.

Next, by applying ultraviolet radiation onto the mask 9, the resin layer4 a revealed from the opening 9 a is exposed. However, in the exposureprocess, the pattern to be formed of the resin layer 4 aobtained afterdevelopment must be a convexity having a curved top surface, which canbe achieved by adjusting exposure conditions. Specifically, exposure isconducted at an exposure value sufficiently lower than the standardexposure value for the material and thickness of the resin layer 4 a,what is called underexposure. In addition, the actual exposure(underexposure) is conducted at, for example, approximately half thestandard exposure value.

When exposure is conducted as described above, the exposure valueapplied on the resin layer 4 a revealed from the opening 9 a of the mask9 gradually becomes smaller going outward from the center of the opening9 a. Therefore, when development is conducted after such an exposureprocess, an unexposed region created on the resin layer 4 a, revealedfrom the opening 9 a, due to a small exposure value is developed andremoved. That is, in accordance with the extent of exposure on thesurface of the resin layer 4 a, which gradually decreases from thecenter to the periphery of the opening 9 a, the unexposed region createdby the decrease in the extent of exposure is developed and removed. As aresult, as shown in FIG. 5, the resin layer 4 a forms a pattern of aconvexity having a curved top surface, in other words, the protrusion 4taking the shape of an approximate beheaded pyramid.

After forming the protrusion 4 by removing the unexposed region of theresin layer 4 a as described above, a conductive material (which becomesthe first conductive layer by patterning) comprising metals such as Au,TiW, Cu, Cr, Ni, Ti, W, NiV, Al, Pd, Pb-free solder, or the like isdeposited on the entire surface of the substrate 1, including theelectrode 2 formed by being revealed from the opening of the protectivefilm 3 and the protrusion 4, by sputtering, as shown in FIG. 6. Thethickness of a conductive material layer 6 (a conductive layer) isapproximately 200 μm, for example.

Next, a photoresist layer is formed by applying photoresist on theentire surface of the conductive material layer 6 by spin coating,dipping, spray coating, or the like. Then, the photoresist layer ispatterned in a specified shape by exposure and development using a maskcorresponding to the top-view shape (top-view pattern) of the firstconductive layer 5 to be formed. Thus, as shown in FIG. 7, a photoresistpattern 14 is formed corresponding to the pattern shape of the firstconductive layer to be formed.

Then, the region of the conductive material layer 6 that is not coveredwith the photoresist pattern 14 is removed by etching. Thus, as shown inFIG. 8, the first conductive layer 5 electrically coupled to theelectrode 2 is formed covering the protective film 3 including theopening formed in the protective film 3 and spreading over theprotrusion 4. In addition, the etching method employed here can be anymethod: for example, dry etching using plasma, wet etching using achemical solution, or the like.

Lastly, by removing the photoresist pattern 14 as shown in FIG. 9 andfurther cutting into pieces by dicing, if needed, a semiconductor device10 according to the present invention can be obtained.

Second Embodiment

The second embodiment will now be described in detail referring to theaccompanying drawings.

In the method for forming a semiconductor device according to the firstembodiment, the conductive unit covering from the electrode 2 andspreading over the surface of the protrusion 4 is formed with a singlelayer of the first conductive layer 5. In contrast, the secondembodiment provides a different method wherein the conductive unitcovering from the electrode 2 and spreading over the surface of theprotrusion 4 is formed with two layers including the first conductivelayer 5 and the second conductive layer 7. In addition, the otherdetails of the method for forming a semiconductor device are the same asthose of the first embodiment. Therefore, the same reference numeralsare used for the components common to both embodiments and detaileddescription is omitted.

First, employing the manufacturing steps shown in FIGS. 2 to 6 of thefirst embodiment, an electrode 2, a resin protrusion 4 projecting higherthan the electrode 2, and a conductive material layer 6 (a layer tobecome the first conductive layer in the latter description) that iselectrically coupled to the electrode 2 and covers the surface of theprotrusion 4 are formed on a substrate 1.

Next, as shown in FIG. 10, photoresist is applied on the entire surfaceof the conductive material layer 6 by spin coating, dipping, spraycoating, or the like to form a photoresist layer. Then, the photoresistlayer is patterned into a specified shape by exposure and development(photolithography) to the photoresist layer using a mask correspondingto the top-view shape (top-view pattern) of the second conductive layer7. Thus, as shown in FIG. 10, a photoresist pattern 11 having an openingshape corresponding to that of the second conductive layer 7 to beformed is formed.

Then, as shown in FIG. 11, electrolytic plating is performed using theregion of the conductive material layer 6 that is not covered with thephotoresist pattern 11, that is, the revealed conductive material layer6, as a seed layer. A plating layer such as Au, Cu, or the like isdeposited on the conductive material layer 6, by electrolytic plating,to form the second conductive layer 7. Here, the film thickness of thesecond conductive layer 7 must be thicker, 1 to 2 μm for example, thanthat of the first conductive layer 5. When the film thickness of thesecond conductive layer 7 is less than 1 μm, the film strength becomesweak and causes wire breakage, or the like because the first conductivelayer 5 and the second conductive layer 7 cannot follow thetransformation of the protrusion 4 occurring at the time of hot pressingfor bonding. On the other hand, when the film thickness of the secondconductive layer 7 is over 2 μm, the film strength is enhanced becausethe layer becomes thicker. However, the time required for platingbecomes longer and pitch narrowing becomes difficult.

Next, as shown in FIG. 12, the photoresist pattern 11 remaining on theconductive material layer 6 is removed. Then, the region of theconductive material layer 6 that is not covered with the secondconductive layer 7, that is, the region to become a non-conductive unit,is removed by etching. The etching must be conducted by selectivelyremoving the region of the conductive material layer 6 that is notcovered with the second conductive layer 7, using the second conductivelayer 7 as a mask. Both methods of dry etching and wet etching areavailable. Thus, the first conductive layer 5 that is patterned inalmost the same shape as the second conductive layer 7 is formed. Withsuch a method, a laminated conductive unit comprising the firstconductive layer 5, covering from the electrode 2 and spreading over thetop of the protrusion 4, and the second conductive layer 7 are formed.Further, in the present embodiment, an external electrode 8 is formed ofthe protrusion 4 as well as the first conductive layer 5 and the secondconductive layer 7 laminated on the protrusion 4. After the aboveprocess, by dicing for cutting into pieces, if needed, a semiconductordevice 10 according to the present invention can be obtained.

Electro-optic device

Next, a method for manufacturing a liquid crystal display device bymounting the semiconductor device 10, manufactured with the abovemanufacturing method, onto a wiring board, for example, of a liquidcrystal display device (an electro-optic device) will be described indetail referring to the accompanying drawings. As a mounting method tobe employed, chip-on-glass (COG) coupling is suitable.

FIG. 13 is an example drawing of a COG liquid crystal display device. Asshown in FIG. 13, a liquid crystal display device 50 as an electro-opticdevice comprises: a frame-shaped shield case 68 formed of a metal plate;a liquid crystal panel 52 as an electro-optic panel; an LSI 58 fordriving liquid crystal; an ACF (not illustrated) for electricallycoupling the liquid crystal panel 52 and a bump formed on the activesurface of the LSI 58 by COG mounting; and a retaining member 172 forretaining the overall device strength.

Further, the liquid crystal panel 52 comprises a wiring board 20 and anopposed board 53 that is placed facing the wiring board 20. On thewiring board 20, which is configured of a glass substrate, or the like,there are a plurality of scanning lines and data lines formed in amatrix; switching elements (not illustrated) coupled to the scanning anddata lines; pixel electrodes (not illustrated) coupled to the switchingelements; and a plurality of electrode terminals 22 formed correspondingto the arrangement of the plurality of external electrodes 8 of thesemiconductor device 10.

FIG. 14 is an enlarged cross-sectional view of the part where thesemiconductor device 10 is mounted on the wiring board 20 by COGmounting. First, a bonding material 24 for coupling the externalelectrode 8 formed on the semiconductor device 10 and the electrodeterminal 22 formed on the wiring board 20 is placed on the wiring board20. The bonding material can be placed on the semiconductor device 10 oron both the semiconductor device 10 and the wiring board 20. Further, inthe present embodiment, non-conductive paste (NCP) bonding is employedfor coupling the external electrode 8 of the semiconductor device 10 andthe electrode terminal 22 of the wiring board 20. Therefore, NCF, whichis a dielectric resin, is used as the bonding material 24. The NCF,which contains thermosetting epoxy resin, has a glass transitiontemperature of around 220 degrees Celsius.

Next, the semiconductor device 10 is bonded on the wiring board 20 onwhich the NCP bonding material 24 is placed. The semiconductor device 10is bonded by matching the positions of the external electrode 8 of thesemiconductor device 10 and the electrode terminal 22 of the wiringboard 20. Then, hot pressing of the semiconductor substrate 1 and thewiring board 20 is conducted within the temperature range of 200 degreesCelsius to 260 degrees Celsius using a flip-chip bonder. The mountingtemperature should be set within the above range because, when themounting temperature is less than 200 degrees Celsius, the elastic forceof the resin forming the external electrode 8 of the semiconductordevice 10 does not start to decrease and resin transformation does notoccur. On the other hand, when the mounting temperature is greater than260 degrees Celsius, the elastic force of the resin forming the externalelectrode 8 is low and, before the resin makes a transformation, the NCPbonding material 24 is hardened, leading to poor coupling. Therefore, inthe present embodiment, a resin having a glass transition temperature ofapproximately 220 degrees Celsius, which is within the above mountingtemperature range, is used for forming the external electrode 8 of thesemiconductor device 10 so that mounting can be conducted while theelastic force of the resin is decreasing.

FIG. 15 is a graph of the relation between elastic modulus and mountingtemperature when acrylic resin is used as the resin forming theprotrusion 4. The horizontal axis of the graph indicates the transitionof mounting temperature (° C.) and the vertical axis indicates thetransition of elastic force (Pa) of the resin, which are expressed in alogarithmic form. Further, the temperature measurement starts from 30degrees Celsius and ends at 300 degrees Celsius. In addition, theheating rate is 4 degrees Celsius/min. As shown in FIG. 15, the elasticmodulus of the acrylic resin starts to decrease around the mountingtemperature of 170 degrees Celsius. Further, with the rise of themounting temperature, the elastic modulus of the resin keeps decreasing.Within the mounting temperature range of 200 degrees Celsius to 260degrees Celsius, the elastic modulus of the resin shows a decreasebecause the glass transition temperature of the acrylic resin is aroundapproximately 220 degrees Celsius. Therefore, under the pressurizationby the flip chip bonder, the protrusion 4 made of acrylic resin startstransformation before the NCP bonding material 24 starts to be hardened,that is, before the mounting temperature reaches 260 degrees Celsius.

Hot pressing is conducted for 5 to 10 seconds, for example, so as toelectrically couple the external electrode 8 of the semiconductor device10 and the electrode terminal 22 of the wiring board 20 by transformingthe resin protrusion 4. Then, by hardening the NCP bonding material 24,the coupling is fixed and retained. Thus, as shown in FIGS. 13 and 14,the semiconductor device 10 is bonded on the wiring board 20 by COG.

With such a configuration, wherein hot pressing is conducted within thetemperature range including the glass transition temperature of theresin, the elastic modulus of the resin protrusion 4 shows a decrease ata temperature for mounting the semiconductor device 10 on the substrate1. Therefore, the external electrode 8 comprising the protrusion 4 ofthe semiconductor device 10 makes a transformation, assuring thecoupling between the substrate 1 and the electrode terminal 22. As aresult, the problem of poor conduction can be solved and the couplingreliability can be improved. Further, the availability of the NCPcoupling method eliminates the need of using a bonding materialcontaining anisotropic conductive particles, which leads to a costreduction. In addition, manufacturing of the protrusion 4 using a resinhaving a higher room-temperature elastic modulus becomes possible. As aresult, the choice of available resin materials is widened to includeless expensive materials, which also leads to a cost reduction.Furthermore, since the elastic modulus of the resin at the time ofmounting is reduced by using the resin described above as the protrusion4, mounting at a lower load becomes possible. With such a method, theprotrusion 4 can be formed on a region including a switching element,and the like of the semiconductor device 10. Thus, the protrusion 4 canbe formed on any region of the semiconductor device 10 whether or notthere is a switching element present. In addition, in the case offorming the protrusion 4 on a region including a switching element, andthe like, the region where the protrusion 4 is formed in theconventional technique can be reduced, enabling the miniaturization ofsemiconductor devices.

FIG. 16 is a perspective view of the schematic configuration of a liquidcrystal display device manufactured with a different configuration fromthat of the liquid crystal display device described above. The liquidcrystal display device shown in FIG. 16 comprises a color liquid crystalpanel 51 as an electro-optic panel and a chip-on-film (COF) circuitboard 100 coupled to the liquid crystal panel 51. The circuit board 100comprises a semiconductor device 101 manufactured with theabove-described method for manufacturing a semiconductor device. In sucha configuration, the circuit board 100 is an embodiment of the circuitboard according to the present invention, and the liquid crystal displaydevice is an embodiment of the electro-optic device according to thepresent invention. Further, in the liquid crystal display device, anillumination device such as a backlight, or the like and other relatedequipment can be added to the liquid crystal panel 51 according to need.Furthermore, the circuit board 100 is not limited to a COF circuit boardbut can be a chip-on-board (COB) circuit board.

In addition, the present invention can be applied to, other than the COFor COB circuit board, an electro-optic device employing thechip-on-glass (COG) method wherein a driver IC, or the like are directlybonded on a display panel (a liquid crystal panel).

Also, the present invention can be applied to electro-optic devices,other than liquid crystal display devices, such as organic EL displaydevices. FIG. 17 is a cross-sectional view of an organic EL panelprovided on an organic EL display device as the electro-optic deviceaccording to the present invention. An organic EL panel (anelectro-optic panel) 30 is schematically configured by forming a thinfilm transistor (TFT) 32 to form a matrix and further forming aplurality of laminated bodies 33 on a substrate 31. The TFT 32 comprisesa source electrode, a gate electrode, and a drain electrode. The gateelectrode and the source electrode are electrically coupled to theexternal electrode 8 shown in, for example, FIG. 1. The laminated bodies33 include an anode layer 34, a hole injection layer 35, a luminouslayer 36, and a cathode layer 37. The anode layer 34 is coupled to thedrain electrode of the TFT 32, wherein an electric current is suppliedto the anode layer 34 via the source and drain electrodes of the TFT 32when the TFT 32 is turned on.

In the organic EL panel 30 having the above configuration, a lightgenerated by reunification, occurring within the luminous layer 36, of ahole injected from the anode layer 34 into the luminous layer 36 via thehole injection layer 35 and an electron injected from the cathode layer37 into the luminous layer 36 is emitted from the side of the substrate31.

Next, an electronic device on which the electro-optic device accordingto the present embodiment is bonded will be described in detail. Byincorporating electronic parts such as a mother board, a keyboard, ahard disk, and the like that form the liquid crystal display device asthe above-described electro-optic device, a central processing unit(CPU), and the like into a chassis, a notebook personal computer 60 (anelectronic device), for example, shown in FIG. 18 can be manufactured.

FIG. 18 is an external view of a notebook computer as an electronicdevice according to an embodiment of the present invention. In FIG. 18,a reference numeral 61 indicates a chassis, a reference numeral 62indicates a liquid crystal display device (an electro-optic device), anda reference numeral 63 indicates a keyboard. Further, in FIG. 18 showinga notebook computer having a liquid crystal display device, the liquidcrystal display device can be substituted by an organic EL displaydevice.

In addition, the above embodiment is not limited to a notebook computer,which is taken as an example of the electronic device, but can beapplicable to electronic devices such as cellular phones, liquid crystalprojectors, multimedia-compatible personal computers (PCs) andengineering workstations (EWSs), pagers, word processors, televisions,videotape recorders with a viewfinder or a direct-view monitor,electronic organizers, electronic desk calculators, car navigationdevices, POS terminals, devices having a touch panel, and the like.

The present invention is not limited to the above embodiments describinga semiconductor device and a method for manufacturing the same, as wellas an electro-optic device and an electronic device, but can be freelyvaried within the scope of the present invention.

For example, the “semiconductor element” described in one of the aboveembodiments can be substituted by an “electronic element” to manufacturean electronic part. Electronic parts manufactured using such anelectronic element include, for example, optical elements, resistors,condensers, coils, oscillators, filters, temperature sensors,thermistors, varistors, volumes, fuses, and the like.

1. A method of forming a bonded structure, comprising the steps of:providing a semiconductor device onto a substrate with an intermediaryof a bonding material, the semiconductor device having: an electrode; aconvexity protruding higher than the electrode and formed of a resin;and a conductive unit electrically coupled to the electrode andextending over a surface of the convexity; and forming the bondedstructure by hot pressing within a temperature range including a glasstransition temperature of the resin.
 2. The method of forming a bondedstructure according to claim 1, wherein the temperature of forming thebonded structure is at least equal to a temperature at which an elasticmodulus of the resin decreases.
 3. The method of forming a bondedstructure according to claim 1, wherein the resin to be used furthercomprises polyimide and the temperature of forming the bonded structureis between 200 degrees Celsius and 260 degrees Celsius inclusive.
 4. Themethod of forming a bonded structure according to claim 1, wherein theresin further comprises one of acrylic resin and phenolic resin.
 5. Themethod of forming a bonded structure according to claim 1, furthercomprising the steps of: providing a plurality of the electrodes;forming a series of the convexities on the plurality of electrodes, theconvexities being adjacent to each other; forming the conductive unit ona surface of the convexities corresponding to each of the electrodes;and electrically coupling the conductive unit and the electrode.
 6. Themethod of forming a bonded structure according to claim 1, wherein thestep of forming the conductive unit further comprises the steps of:forming a conductive layer by sputtering; and forming a first conductivelayer by patterning the conductive layer, the first conductive layerbeing coupled to the electrode and extending over a surface of theconvexity.
 7. The method of forming a bonded structure according toclaim 6, wherein the step of forming the conductive unit furthercomprises the steps of: forming a second conductive layer on theconductive layer by plating; and forming a first conductive layer byremoving part of the conductive layer that is not covered with thesecond conductive layer.
 8. The method of forming a bonded structureaccording to claim 1, wherein the bonding material further comprises anon-conductive bonding material.
 9. A circuit board comprising asemiconductor device manufactured by the method of forming a bondedstructure according to claim
 1. 10. An electro-optic device comprisingthe circuit board according to claim
 9. 11. An electronic devicecomprising the electro-optic device according to claim 10.